Fabric interlining adhesives are used on fusible interlinings, which are materials such as fabric which have been coated on one side with a discontinuous pattern of adhesive. When the interlining is bonded to a face fabric in a garment, it provides body and shape to the garment without impairing the ability of the fabric to breathe. Fusible interlinings are used in the manufacture of suits, in shirt collars and cuffs, and in the waistbands of trousers. In the manufacture of suits, polycarbonate basting threads are frequently used to temporarily hold the parts of the suit in place. After the suit is completed, a solvent such as perchloroethylene or trichloroethylene is used to embrittle the polycarbonate thread so that it may be brushed from the fabric.
Binder fibers are used with nonwovens, which are formed from matrix fibers into a web, sheet, or mat. The binder fibers give strength to the web, mat, or sheet by bonding it together. The most common binder elements in use today are the water-based latexes. These latexes have poor adhesion to synthetic and natural fibers and require as much as 50% by weight add-on of cured latex to impart useful strength to the nonwovens. Also, most of the latexes contain melamine crosslinking components which undesirably emit formaldehyde when cured. Other bonding media used, although in much smaller quantities, are binder fibers. The binder fibers now used are polyolefin, polypropylene, poly ethylene, and copolymers of the two, or partially oriented poly(ethylene terephthalate) or copolyesters of poly(ethylene terephthalate). The polyolefin binder fibers have poor adhesion to nonwoven matrix fibers which are not polyolefin and require very high add-on even when used to bond polyolefin fibers. The polyester and copolyesters used are partially oriented fibers which require relatively high bonding temperatures and have very narrow temperature ranges for bonding, because of their tendency to crystallize as the bonding temperature reaches the glass transition temperature of the binder fiber. These fibers cannot be melted or rendered molten because they have approximately the same melting temperature or flow temperature as the high melting polyester matrix fiber and a much higher melting temperature than the polyolefin matrix fiber. To use these high temperatures would cause the matrix fiber to form a film sheet with no esthetic resemblance to a fabric. Partially oriented binder fibers must be bonded quickly within a very narrow temperature range as the temperature of the fiber reaches the softening point of the partially oriented fiber and before the fiber crystallizes. Once the fiber crystallizes, it must be heated above its crystalline melting point before it can be bonded and this temperature is usually high enough to destroy the fiber integrity of the matrix fiber.
I have now discovered a family of copolyesters which are useful as fusible interining adhesives and binder fibers. These copolyesters can be spun into fibers that are exceptionally useful for blending with matrix fibers, and which can be bonded over a wide range of temperatures to impart strength and esthetic properties. These copolyester adhesives have excellent adhesion to polyolefin, polyester, polyamide, and cellulosic fibers such as paper. Fibers of these copolyesters can be blended with matrix fibers by either wet lay, dry lay, or air lay processing. They are bondable over a wide range of temperatures and pressures to form fabrics or sheets which are smooth like film or high loft battings. The copolyesters give bond strength equivalent to other known binder fibers at much lower loading weights.
Certain polyesters are known to be useful for fusible interlining adhesives and binder fibers. However, these polymers also tend to have certain disadvantages. For example, one polyester of interest is the copolyester of terephthalic acid, adipic acid, ethylene glycol and 1,4-butanediol as described in U.S. Pat. No. 3,699,921. Such polyesters tend to block in pellet form and fumed silica must be added in significant amounts to make it possible to grind this polymer into powder. Excessive amounts of fumed silica in the powder, however, prevent good coatability and good fusion of the powders on the fusible interlining fabric when applied with powder point applicators.
Copolyesters generally have lower melting points than homopolyesters. For example, the melting point of a polyester of terephthalic acid and ethylene glycol is around 260.degree. C. A polyester consisting of 90 mole % of terephthalic acid and 10 mole % of isophthalic acid in which ethylene glycol has been used as the diol component, has a melting point of 236.degree. C. When the molar ratio of terephthalic acid to isophthalic acid is 80:20, a copolyester is obtained which has a melting point of 210.degree. C. When the ratio of terephthalic acid to isophthalic acid is 70:30 the melting point drops to 185.degree. C.
Conditions are similar when ethylene glycol is replaced by 1,4-butanediol. A polybutylene terephthalate comparable to polyethylene terephthalate has a melting point of 225.degree. C.
In German Offenlegungsschrift No. 1,920,432 there is disclosed a dry-cleaning, fluid resistant polyester fusion adhesive prepared from (1) terephthalic acid and ethylene glycol, (2) adipic acid and 1,4-butanediol. The degree of crystallization of this copolyester, however, is already so low that it is not suitable for a fusion adhesive. Disadvantages reside in both the surface stickiness of the coated substrate and the stickiness of the copolyesters which is considerable even at room temperature. Copolyesters of this type are not suitable for the preparation of adhesives in powder form.
U.S. Pat. No. 4,252,940 discloses copolyester adhesives of terephthalic acid together with isophthalic, succinic, adipic or glutaric, and a blend of 1,6-hexanediol and diethylene glycol.
Other copolyester fabric adhesives are disclosed in my U.S. Pat. No. 4,330,670. This patent discloses copolyesters derived from 1,4-cyclohexanedicarboxylic acid and 1,4-butanediol and optional second acids or glycols.
It is well known in the art that the crystallinity of a polyester is one parameter which may be used to determine solvent resistance, i.e., the more amorphous (less crystalline), the more susceptible to dry-cleaning solvents the polyester will be. Also, glass transition temperature is a parameter by which the temperature at which a polyester, even an amorphous polyester, will be affected by a solvent.
It is also known that modification of a homopolyester by copolymerization with other acid or glycol moieties or combinations of glycol and acid moieties to form copolymers or terpolymers drastically reduces or eliminates crystallinity. The crystallinity of copolyesters is also dependent on the particular comonomers from which the copolyester is synthesized. For example, a polyester of terephthalic acid and 1,4-butanediol (even number of carbon atoms) will crystallize more readily than a polyester prepared from terephthalic acid and either 1,3-propanediol (odd number carbon atoms) or 1,5-pentanediol (odd number of carbon atoms). The crystallization phenomenon of copolyesters, expecially those that are low melting, below 150.degree. C., is unpredictable.
Amorphous polyesters cannot be used as fusion adhesives in which resistance to dry-cleaning agents and high set-up speed are required. In like manner, those polyesters are undesirable which have too little crystallinity, because they solidify too slowly and consequently do not lose their surface stickiness for long periods of time.
Other copolyesters of interest are those disclosed in U.S. Pat. Nos. 4,094,721; 3,948,859; 4,012,363; and 3,853,665.